1. Field of the Invention
The present invention relates to a twin-core ferrule structure for an optical fiber connector and particularly, to a twin-core ferrule structure which is small in size and improved in high-volume productivity.
2. Description of the Prior Art
It is common for fitting two optical fibers in parallel at a desired position to insert and bond the two optical fibers into their respective single-core ferrules and then arrange in parallel and join the two single-core ferrules to each other. FIG. 5 is a longitudinally cross sectional view of the two single-core ferrules arranged in parallel. As shown, the single-core ferrules are denoted by 51 and 61 having the same structure. For ease of the description, the single-core ferrule 51 will be explained herein while identical components of the single-core ferrule 61 to those of the single-core ferrule 51 are denoted by parenthesized numerals. The single-core ferrule 51 (61) has a structure which comprises a cylindrical sleeve 54 (64) having a cylindrical hole 55 (65) provided in the front region of a medium-diameter circular cylindrical body hereof for accepting a capillary 52 (62) and a cylindrical hole 56 (66) provided in the rear region thereof, of which inner diameter is substantially identical to that of the cylindrical hole 55 (65), for accepting an optical fiber core, and the capillary 52 (62) having a fitting hole 53 (63) provided axially in a small-diameter circular cylindrical body thereof for accepting an optical fiber element. In the structure, the capillary 52 (62) is pressed into the cylindrical hole 55 (65) in the front region of the cylindrical sleeve 54 (64). In the conventional single-core ferrule 51 (61), the cylindrical sleeve 54 (64) is fabricated by cutting a stainless steel material, and the capillary 52 (62) is shaped by sintering a powdered zirconia (ZiO.sub.2). The single-core ferrule 51 is joined in parallel with the single-core ferrule 61 and their resultant assembly is used as a twin-core ferrule 50.
An example of the twin-core ferrule 50 composed of two parallel joined single-core ferrules may be provided in which, when the optical fiber element having a diameter of 125 .mu.m is employed, the diameter of the optical fiber element fitting hole 53 (63) in the capillary 52 (62) is 126 .mu.m, the outer diameter of the capillary 52 (62) is 1.4 mm, the diameter of the cylindrical holes 55 (65) and 56 (66) in the front and rear regions of the cylindrical sleeve 54 (64) is 1.4 mm, the outer diameter of the cylindrical sleeve 54 (64) is 2.5 mm, the width of the two single-core ferrules 51 and 61 joined in parallel is 5.0 mm, and the distance D2 between the centers of the two optical fiber element fitting holes 53 and 63 is 2.5 mm.
In such a conventional twin-core ferrule consisting of two parallel joined single-core ferrules, the distance between its two optical fiber element fitting holes is determined by the outer diameter of the cylindrical sleeves. Reducing the distance between the two optical fiber element requires a decrease in the outer diameter of the cylindrical sleeves, but the decrease has a limit. This retards the miniaturization of the overall dimensions of optical connectors while relevant optical components have successfully been decreased in size. Also, the cylindrical sleeve of any conventional ferrule is fabricated by cutting a stainless steel material and will hardly be advantageous for high-volume production. Although the ferrule is intended to have an improved shape for miniaturizing its size and enhancing its functions, its shape is tailored through cutting process and will thus be limited in design and dimensions.